1. Field of the Invention
The present invention relates generally to a method for rendering a substrate resistant to plasma erosion. More particularly, the present invention relates to such a method in which there is used cured polymers of compounds comprising silicon atoms linked together by a hydrocarbon chain and further comprising phenyl groups substituted with a glycidyl group.
2. Description of the Background Art
Epoxy resins are widely used as adhesives, encapsulants, and coatings for a variety of applications. In particular, for application to structural and electronic devices, epoxy resins are useful since they provide mechanical protection, good substrate adhesion, thermal and oxidative stability, and moisture resistance. In addition, compliance is a highly desirable property for these resins since it allows the dissipation of stress that accompanies thermal and mechanical cycling of the encapsulant. Furthermore, enhanced toughness provides mechanical protection against fracture damage. However, state-of-the-art systems exhibiting such compliance generally possess poor thermal stabilities. Another important property is the repairability of the adhesive, coating, or encapsulant. As expected, a rigid system is generally more difficult to repair and replace than a ductile one.
One group of epoxy resins particularly useful for electronic applications consists of epoxysilicone compounds, which are compounds comprising silicon atoms joined together by oxygen linkages and further comprising terminal glycidyl groups. Such epoxysilicone compounds have been known for many years and are described, for example, in the publications by Bilow, Lawrence and Patterson, "Synthesis and Polymerization of 1,3-bis (2,3-epoxypropylphenyl)tetramethylsiloxanes and Related Compounds, Journal of Polymer Science, Volume 5, 1967, pages 2595 to 2615 and by Patterson and Bilow, "Polymers from Siloxane-Containing Epoxides," Journal of Polymer Science, Volume 7, 1969, pages 1099 to 1110. As described in these references, such epoxysiloxane compounds were prepared by reacting the Grignard reagent derivable from an allylbromobenzene with a large excess of dichlorodimethylsilane. The resulting compound, chlorodimethyl(allylphenyl)silane, must be isolated from excess dichlorodimethylsilane by repeated distillation steps. chlorodimethyl(allylphenyl)silane was then hydrolyzed to give 1,3-bis(allylphenyl)-1,1,3,3-tetramethyl-1,3-disiloxane. Epoxidation was effected either with 3-chloroperoxybenzoic acid or trifluoroperoxyacetic acid. However, such a procedure is not only tedious, but also yields a product contaminated by impurities produced by rearrangement or reversion in which --Si--O-- groups break away from the rest of the molecule and form macrocyles or higher linear chains. In addition, the corrosive trifluoroperoxyacetic acid was difficult and dangerous to prepare on a large scale, and the 3-chlorobenzoic acid side product generated in the epoxidation reaction was so soluble in the desired product that complete removal of this acid residue was impossible. Furthermore, such a process is not conducive to tailor making the length of the siloxane chain.
When epoxy resins are used in structural applications for outer space, such as for adhesives or coatings in satellite components, the resin must not only be able to withstand the temperature extremes encountered in space, for example -148.degree. F. (-100.degree. C.) to 212.degree. F. (100.degree. C.), for extended periods of time, such as several years, but also be able to withstand the higher temperatures (350.degree. F. or 177.degree. C.) encountered in rigorous space applications for shorter periods of time. In addition, the material must meet the National Aeronautics and Space Administration (NASA) outgassing requirements, i.e., &lt;1% total mass loss, and .ltoreq.0.10% collectible volatile condensable materials, to insure that the material does not release gaseous component substances which would undesirably accumulate on other spacecraft parts in the outer-space vacuum.
Moreover, structures which are exposed to low earth orbit, such as satellites or shuttles, must be able to resist the erosion caused by the plasma encountered in such as environment, particularly elemental oxygen. Non-resistant materials are eroded away by the plasma, with resultant loss of structural integrity and performance. Silicone materials are commonly used to provide plasma resistance but have the disadvantage of being easily abraded physically.
Furthermore, it would be advantageous to have a material for space applications, as well as other uses, which provides reduction of the vibration experienced by structural devices mounted on a platform and by electronic components mounted on a substrate. Such vibration would adversely affect performance of the structures and components. Materials which provide this reduction in vibration energy are known as "damping materials" and function by dissipating the vibration energy to produce a reduction or decay of motion. Materials commonly used for this purpose include hydrocarbon and silicone elastomers. The former materials have the advantages that their thermal strability is low and their processibility is limited, while the latter materials have the advantage of poor abrasion resistance.
Heretofor, ductile, processible epoxy resins meeting all of the previously discussed requirements have been unobtainable.
Thus, a need exists for an epoxy resin for electronic and structual space applications which is tough, thermally and oxidatively stable, repairable, resistant to moisture, and which possesses low outgassing characteristics. In addition, a need exists for the preparation of the .psi., .omega.-alkenyl compounds from which such epoxy resins, among others, may be formed. (The next to the lowest homolog of the .psi., .omega.-alkenyl group is the allyl group from which the glycidyl group is derived.) A further need exists for such epoxy resins which are resistant to erosion by oxygen plasma. Yet another need exists for such epoxy resins which provide vibration damping to protect structural devices and electronic components.